1. Field of the Invention
The present invention relates to methods of combating lost drilling fluid circulation in wells, and more particularly, to such methods wherein cementitious plugs are formed in subterranean drilling fluid thief zones.
2. Description of the Prior Art
In the drilling of wells through naturally fractured formations, lost drilling fluid circulation problems are often encountered. That is, as subterranean vugs, fractures and other thief zones are encountered during the drilling of a well bore, drilling fluid circulation is often lost and drilling operations must be terminated while remedial steps are taken. Such problems are pronounced in the drilling of geothermal wells which are usually drilled in highly vugular and/or fractured formations.
Heretofore, drilling fluid thief zones encountered in the drilling of wells have been plugged utilizing conventional hydraulic cement compositions, e.g., Portland cement compositions. While such cement plugs can be made to work successfully, the time required for allowing the cement composition to cure and then drilling the well bore through the cured plug makes the plugging operation very uneconomical. Additionally, when the well bore is drilled through such plugs, the high lime content cement cuttings produced often adversely react with drilling fluid in contact therewith whereby the rheology of the drilling fluid is changed. This in turn requires drilling fluid conditioning before normal drilling operations are resumed.
Thus, there is a need for improved methods of combating lost drilling fluid circulation into subterranean thief zones whereby the thief zones can be rapidly plugged without affecting the rheology of the drilling fluid to thereby reduce rig time and drilling fluid conditioning expense.